STY: Normalize styles across installations via .dir-locals.el

For Emacs users, set a .dir-locals.el file to define behavior during
formatting operations like `fill-paragraph`

Set:
- Double spaces after sentences. (Which is the default.)
- Fill column to 79 characters. (To match pep8 script.)
- Docstrings to conform to Django formatting, since that is currently
  most alike to the existing docstrings.